| Titanium alloy is extremely limited in its use fields due to low hardness and poor wear resistance.The traditional gas carburizing technology has the disadvantages of high reaction temperature,long cycle required,low carburizing efficiency,and easy deformation of the workpiece,which cannot fully solve the actual demand of titanium alloy.In this paper,the surface strengthening of TA2 titanium alloy is carried out by vacuum pulse carburizing and vacuum pulse induction carburizing technology.The microstructure,structure and wear resistance of the obtained graded carburized layer were studied by X-ray diffractometer,optical microscope,scanning electron microscope,XPS,automatic microhardness tester and end face wear tester.L9?33?orthogonal experiment is used to investigate the effects of temperature,pressure and atmosphere ratio on the hardness,thickness and wear resistance of TA2titanium alloy carburized layer and optimize the TA2 titanium alloy gap vacuum carburizing process.The results show that under the two processes of vacuum pulse carburizing and vacuum pulse induction carburizing,the changes of hardness,thickness and wear resistance of the layer are consistent.The influence of each factor is temperature,methane acetylene atmosphere ratio and pressure from high to low.The optimum process parameters obtained by orthogonal test are 940? of temperature,-70 KPa of pressure,and methane and acetylene ratio of 7:1.The subseuent vacuum pulse carburizing and vacuum induction pulse carburization,a uniform TiC phase is formed on the surface of TA2 titanium alloy.The carburized layer can be quickly obtained by vacuum pulse induction carburization,which can reach 22?m in 15 min,108?m in 2 hours,and the surface hardness reaches 1070.5HV0.025.After 8 hours carburization test,the vacuum tube furnace has a thickness of 96?m and a hardness of 947.5 HV0.025.The vacuum pulse carburizing and vacuum pulse induction carburizing kinetics are studied by the self-built model of the research group.Data fitting analysis shows that the vacuum pulse carburizing of TA2 titanium alloy is mainly controlled by"internal diffusion".The apparent activation energy is 265.0 kJ/mol,and reaches 150?m at 940?.The“target carburization depth”is expected to be 1109 min;the vacuum pulse induction carburization process is controlled by“surface adsorption”and“internal diffusion”.The apparent activation energy is 198.45 kJ/mol,and the time to reach the same“target carburization depth”at the same temperature is expected to be only 168 min,and the efficiency is much higher than the former process.As the carburizing time increases,the wear resistance of the TA2 titanium alloy also increases.After 2 hours of vacuum pulse induction carburization,the wear amount(7.1×10-4cm3)is only 1/138 of the original.The amount of wear after 8 h vacuum pulse carburization can also reach 1.09×10-3 cm3.The temperature has a great influence on the wear resistance of the carburized layer.The wear resistance of the alloy treated at 940 and 920? is much higher than 900?.Comparing the two processes,vacuum pulse induction carburizing efficiency is higher,and hardness and wear resistance are better than vacuum pulse carburizing. |
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